What is the ruling on a father's pension and the voluntary retirement money he received, when he was previously unaware of its impermissibility, and is now in need of it? And are there any Sharia evidences that permit or prohibit taking voluntary retirement money?

Pension funds are of two types: the cooperative, mutual type, which is often state-affiliated. There is no objection to subscribing to this type and benefiting from what it provides. The other type is commercial, based on gharar (excessive uncertainty or deception) and gambling, and invests funds in prohibited activities. It is forbidden to voluntarily subscribe to this type.

If the pension fund the father subscribed to is of the prohibited type, he is only entitled to what was deducted from his salary. Any surplus must be disposed of by giving it to the poor and needy. If the father himself is poor, he may take what suffices for his needs and the needs of his family. His subscription to it before he knew of its prohibition absolves him of sin and makes permissible for him what he received before knowing of its prohibition.